It has been known for a long time and is well documented in the literature to apply electrically conductive and infrared reflecting tin oxide layers on substrates such as, for example, glass. The preparation of such electrically conductive and infrared reflecting tin oxide layers applied as coatings on substrates is oftentimes accomplished by pyrolytic decomposition of liquid preparations. These liquid preparations essentially contain one or several base tin compounds and one or several suitable fluoride-containing doping compounds.
A large number of publications and patents are in existence which are directed to such electrically conductive and infrared reflecting tin oxide layers which are coated onto substrates. The same applies for the liquid preparations for the preparation of such tin oxide layers.
According to the prior art, the preparations referred to are usually applied to the substrate, such as glass, in a spray-atomizing procedure, the substrate, e.g., the glass, having been previously heated. This results in pyrolytic or pyrogenic decompositions of the compounds contained in the preparations and, in turn, in the deposition on the substrate of the electrically conductive and infrared reflecting tin oxide layers which, thus, become bonded to the substrate.
The electrical conductivity is generated by fault points in the respective tin oxide layers, the fault points being formed for the most part by the added doping agents. In this manner, fault point terms or donor terms are produced only slightly below the conduction band through which, if necessary with slight energy expenditure, electrons can be brought into the conduction band. This, however, is not the case with respect to pure, undoped tin oxide because of the prohibited zone which is present between valence band and conduction band.
Electrically conductive pigments are necessary to generate electrical conductivity or properly to adjust the anti-static properties of a variety of solid and liquid technical products such as, for example, plastics, lacquers, paints, papers, toners and textiles. In addition to metal powders and graphite, which necessarily cause a dark dyeing of such technical products, semi-conductors in powder form are used for this purpose. In so doing, it is desirable to employ semi-conductor pigments which have not only high electrical conductivity or low specific resistance, but which also are as white as possible or at least have a light color and are of fine grain size.
For the indicated purpose it is known to use conductive tin oxides which are doped with antimony. Such antimony doped tin oxides have been used directly and applied on carrier materials such as, for example, titanium oxide. However, such electrically conductive tin oxides have several disadvantages. Due to the doping with antimony, such conductive tin oxides, dependent on the antimony content and the annealing temperature, have a blue color of varying intensity. Moreover, antimony oxide-containing tin oxides as, indeed, generally all antimony oxide-containing materials, carry with them certain health and environmental risks and are therefore not favored at the workplace.